Control apparatus for internal combustion engine

ABSTRACT

A control apparatus for an internal combustion engine according to the invention is applied to an internal combustion engine in which EGR gas and condensed water generated by an EGR cooler are supplied into a cylinder. The control apparatus calculates an equivalence ratio of the internal combustion engine, and controls an EGR valve and a condensed water supply valve such that, when the equivalence ratio is high, a supply rate of the condensed water increases and a supply rate of the EGR gas decreases relative to when the equivalence ratio is low.

TECHNICAL FIELD

The invention relates to a control apparatus applied to an internalcombustion engine having an exhaust gas recirculation (EGR) apparatus.

BACKGROUND ART

A conventional apparatus stores condensed water generated by an EGRcooler in a condensed water tank, and injects the stored condensed waterinto an intake passage (Patent Document 1). The condensed water suppliedto the intake passage is led into a cylinder together with intake airand vaporized in the cylinder, thereby suppressing a combustiontemperature. As a result, an amount of NO_(X) generated in response tocombustion is suppressed. Patent Document 2 may be cited as anotherrelated art document relating to the invention.

Patent Document 1: Japanese Patent Application Publication No. 10-318049(JP 10-318049 A)

Patent Document 2: Japanese Patent Application Publication No.2010-71135 (JP 2010-71135 A)

SUMMARY OF THE INVENTION

The amount of generated NO_(X) can be reduced by supplying EGR gas intothe cylinder. When the amount of supplied EGR is increased, however, anin-cylinder density increases, thereby impairing the diffusion of fuelspray through the cylinder. Hence, when the amount of supplied EGR gasbecomes excessive, a utilization rate of air in the cylinder decreases,and as a result, amounts of generated smoke and hydrocarbon (HC) mayincrease.

An object of the invention is therefore to provide a control apparatusfor an internal combustion engine, with which increases in amounts ofgenerated smoke and HC due to an increase in an in-cylinder density canbe suppressed.

A first control apparatus according to the invention is applied to aninternal combustion engine in which fuel is injected into a cylinder,the internal combustion engine including an EGR apparatus that suppliesa part of exhaust gas into the cylinder as EGR gas, and a low densitysubstance supply apparatus that supplies a low density substance havinga lower density than the EGR gas into the cylinder. The first controlapparatus includes equivalence ratio calculating means for calculatingan equivalence ratio of the internal combustion engine, and supply ratecontrol means for controlling the EGR apparatus and the low densitysubstance supply apparatus such that, when the equivalence ratio ishigh, a supply rate of the low density substance increases and a supplyrate of the EGR gas decreases relative to when the equivalence ratio islow.

According to the first control apparatus, when the equivalence ratio ishigh, the supply rate of the low density substance increases and thesupply rate of the EGR gas decreases relative to when the equivalenceratio is low. Accordingly, the in-cylinder density decreases when theequivalence ratio is high and increases when the equivalence ratio islow. Hence, the in-cylinder density decreases at a high equivalenceratio, and therefore diffusion of the fuel spray can be promoted, withthe result that the amounts of generated smoke and HC can be suppressed.On the other hand, the in-cylinder density increases at a lowequivalence ratio, and therefore a penetration of the fuel spray can bereduced, with the result that increases in cooling loss and an amount ofgenerated HC caused by fuel adhesion to an inner wall surface of thecylinder can be suppressed.

In the first control apparatus, there are no particular limitations on amethod of calculating the equivalence ratio. For example, theequivalence ratio calculating means may calculate the equivalence ratioon the basis of an operating condition of the internal combustionengine.

In an aspect of the first control apparatus, the supply rate controlmeans may control the EGR apparatus and the low density substance supplyapparatus such that the supply rate of the low density substance in acase where the equivalence ratio is lower than a predetermined value islower before warm-up of the internal combustion engine is complete thanafter warm-up of the internal combustion engine is complete. Accordingto this aspect, the in-cylinder density is higher before warm-up of theinternal combustion engine is complete than after warm-up is complete,and therefore the penetration of the fuel spray at a low equivalenceratio can be reduced in comparison with the penetration following thecompletion of warm-up. Hence, fuel adhesion to the inner wall surface ofthe cylinder prior to the completion of warm-up can be suppressed, andas a result, the amount of HC generated prior to the completion ofwarm-up can be reduced.

In an aspect of the first control apparatus, the supply rate controlmeans may calculate the supply rate of the EGR gas and the supply rateof the low density substance on the basis of a fuel injection pressureas well as the equivalence ratio, and then control the EGR apparatus andthe low density substance supply apparatus on the basis of an obtainedcalculation result. The penetration of the fuel spray varies in responseto variation in the fuel injection pressure. According to this aspect,the supply rate of the EGR gas and the supply rate of the low densitysubstance are calculated on the basis of the fuel injection pressure aswell as the equivalence ratio, and therefore the penetration of the fuelspray can be made appropriate.

In an aspect of the first control apparatus, the low density substancesupply apparatus may supply condensed water generated in an exhaustsystem of the internal combustion engine into the cylinder as the lowdensity substance. According to this aspect, the condensed watergenerated in the exhaust system of the internal combustion engine isused, thereby eliminating the need to prepare and resupply a low densitysubstance. Moreover, the supplied condensed water is vaporized in thecylinder, with the result that a combustion temperature decreases. At ahigh equivalence ratio, therefore, the condensed water supply rate isincreased instead of reducing the EGR gas supply rate, and as a result,a NO_(X) generation suppression effect can be maintained whilesuppressing an increase in the in-cylinder density.

A second control apparatus according to the invention is applied to aninternal combustion engine in which fuel is injected into a cylinder,the internal combustion engine including an EGR apparatus that suppliesa part of exhaust gas into the cylinder as EGR gas, and componentproportion modifying means capable of modifying proportions of water andcarbon dioxide in the EGR gas. The second control apparatus includesequivalence ratio calculating means for calculating an equivalence ratioof the internal combustion engine, and component proportion controlmeans for controlling the component proportion modifying means suchthat, when the equivalence ratio is high, a proportion of water in theEGR gas increases and a proportion of carbon dioxide in the EGR gasdecreases relative to when the equivalence ratio is low.

According to the second control apparatus, when the equivalence ratio ishigh, the proportion of water in the EGR gas increases and theproportion of carbon dioxide in the EGR gas decreases relative to whenthe equivalence ratio is low. Accordingly, the in-cylinder densitydecreases when the equivalence ratio is high and increases when theequivalence ratio is low. Hence, the in-cylinder density decreases at ahigh equivalence ratio, and therefore diffusion of the fuel spray can bepromoted, with the result that the amounts of generated smoke and HC canbe suppressed. On the other hand, the in-cylinder density increases at alow equivalence ratio, and therefore the penetration of the fuel spraycan be reduced, with the result that increases in cooling loss and theamount of generated HC caused by fuel adhesion to the inner wall surfaceof the cylinder can be suppressed.

In the second control apparatus, there are no particular limitations onthe method of calculating the equivalence ratio. For example, theequivalence ratio calculating means may calculate the equivalence ratioon the basis of an operating condition of the internal combustionengine.

In an aspect of the second control apparatus, the component proportioncontrol means may control the component proportion modifying means suchthat the proportion of carbon dioxide in the EGR gas in a case where theequivalence ratio is lower than a predetermined value is lower beforewarm-up of the internal combustion engine is complete than after warm-upof the internal combustion engine is complete. According to this aspect,the in-cylinder density is higher before warm-up of the internalcombustion engine is complete than after warm-up is complete, andtherefore the penetration of the fuel spray at a low equivalence ratiocan be reduced in comparison with the penetration following thecompletion of warm-up. Hence, fuel adhesion to the inner wall surface ofthe cylinder prior to the completion of warm-up can be suppressed, andas a result, the amount of HC generated prior to the completion ofwarm-up can be reduced.

In an aspect of the second control apparatus, the component proportioncontrol means may calculate the proportion of water in the EGR gas andthe proportion of carbon dioxide in the EGR gas on the basis of a fuelinjection pressure as well as the equivalence ratio, and then controlthe component proportion modifying means on the basis of an obtainedcalculation result. According to this aspect, the proportion of water inthe EGR gas and the proportion of carbon dioxide in the EGR gas arecalculated on the basis of the fuel injection pressure as well as theequivalence ratio, and therefore the penetration of the fuel spray canbe made appropriate.

In an aspect of the second control apparatus, separating means forseparating carbon dioxide from the EGR gas, adjusting means capable ofadjusting an amount of carbon dioxide separated from the EGR gas, and acondensed water supply mechanism that adds condensed water generated inan exhaust system of the internal combustion engine to the EGR gas fromwhich carbon dioxide has been separated by the separating means may beprovided as the component proportion modifying means. According to thisaspect, the condensed water generated in the exhaust system of theinternal combustion engine is used, thereby eliminating the need toprepare and resupply a low density substance. Moreover, the suppliedcondensed water is vaporized in the cylinder, with the result that thecombustion temperature decreases. At a high equivalence ratio,therefore, the proportion of water in the EGR gas is increased insteadof reducing the proportion of carbon dioxide in the EGR gas, and as aresult, the NO_(X) generation suppression effect can be maintained whilesuppressing an increase in the in-cylinder density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an overall configuration of an internalcombustion engine according to an embodiment of the invention.

FIG. 2 is a view showing a relationship between an equivalence ratio anda penetration.

FIG. 3 is a view showing a characteristic of a calculation map used tocalculate supply rates of EGR gas and condensed water.

FIG. 4 is a view showing a characteristic of a map used to calculate abasic equivalence ratio corresponding to a load.

FIG. 5 is a flowchart showing an example of a control routine accordingto a first embodiment.

FIG. 6 is a flowchart showing an example of a control routine accordingto a second embodiment.

FIG. 7 is a view showing a characteristic of a map used to specify anin-cylinder density.

FIG. 8 is a flowchart showing an example of a control routine accordingto a third embodiment.

FIG. 9 is a view showing a characteristic of a calculation map used tocalculate respective openings of an EGR valve and a condensed watersupply valve from the in-cylinder density specified in FIG. 7.

FIG. 10 is a view showing a characteristic of control according to afourth embodiment.

FIG. 11 is a flowchart showing an example of a control routine accordingto the fourth embodiment.

FIG. 12 is a view showing an overall configuration of an internalcombustion engine according to a fifth embodiment.

FIG. 13 is a view showing a characteristic of a calculation map used tospecify proportions of water and carbon dioxide in the EGR gas.

FIG. 14 is a flowchart showing an example of a control routine accordingto the fifth embodiment.

FIG. 15 is a flowchart showing an example of a control routine accordingto a sixth embodiment.

MODES FOR CARRYING OUT THE INVENTION First Embodiment

As shown in FIG. 1, an internal combustion engine 1A is configured as aseries type four-cylinder diesel engine in which four cylinders 2 aredisposed in a single direction. The internal combustion engine 1A isinstalled in an automobile, for example, as a travel drive source. Afuel injection valve 3 is provided in the internal combustion engine 1Afor each cylinder 2 in order to supply fuel to the cylinders 2. Therespective fuel injection valves 3 are connected to a common rail 5 towhich fuel is pumped, and fuel is supplied to the respective fuelinjection valves 3 through the common rail 5. An intake passage 6 and anexhaust passage 7 are connected to the respective cylinders 2. Theintake passage 6 includes an intake manifold 8 that bifurcates to eachcylinder 2. A compressor 9 a of a turbocharger 9 is provided upstream ofthe intake manifold 8. The exhaust passage 7 includes an exhaustmanifold 10 in which exhaust gas from the respective cylinders 2 iscollected. A turbine 9 b of the turbocharger 9 is provided downstream ofthe exhaust manifold 10. An exhaust gas purification apparatus, notshown in the drawing, is provided on a downstream side of the turbine 9b so that exhaust gas passing through the turbine 9 b is purified by theexhaust gas purification apparatus and then released into theatmosphere.

As shown in FIG. 1, two EGR apparatuses 20A, 20B are provided in theinternal combustion engine 1A in order to implement EGR such that a partof the exhaust gas is recirculated to the intake system as EGR gas inorder to reduce NO_(X) and improve fuel efficiency. The internalcombustion engine 1A uses the two EGR apparatuses 20A, 20B appropriatelyin accordance with a load. The first EGR apparatus 20A is configured asa low pressure loop type EGR apparatus. The first EGR apparatus 20Aincludes a first EGR passage 21 that connects the exhaust passage 7 on adownstream side of the turbine 9 b to the intake passage 6 on anupstream side of the compressor 9 a, a first EGR valve 22 that regulatesa flow of the EGR gas, and a first EGR cooler 23 that cools the EGR gas.The second EGR apparatus 20B is configured as a high pressure loop typeEGR apparatus. The second EGR apparatus 20B includes a second EGRpassage 26 that connects the exhaust manifold 10 to the intake manifold8, a second EGR valve 27 that regulates the flow of the EGR gas, and asecond EGR cooler 28 that cools the EGR gas.

The respective EGR coolers 23, 28 reduce a temperature of the EGR gasusing cooling water of the internal combustion engine 1A as a coolant byperforming heat exchange between the coolant and the warm exhaust gas.When the temperature of the EGR gas is reduced, moisture contained inthe EGR gas condenses, and as a result, condensed water is generated inthe respective EGR coolers 23, 28. A condensed water treatment apparatus30 is provided in the internal combustion engine 1A in order to collectand treat the condensed water generated by the respective EGR coolers23, 28.

The condensed water treatment apparatus 30 includes a condensed watertank 31 that stores the condensed water generated by the respective EGRcoolers 23, 28, a first collection passage 32 that connects the firstEGR cooler 23 to the condensed water tank 31, a second collectionpassage 33 that connects the second EGR cooler 28 to the condensed watertank 31, and a condensed water supply mechanism 35 serving as a lowdensity substance supply apparatus that supplies condensed water CWstored in the condensed water tank 31 to the intake system of theinternal combustion engine 1A. The condensed water supply mechanism 35includes a condensed water passage 36 that connects the condensed watertank 31 to the intake manifold 8 of the intake passage 6. An electricpump 37 and a condensed water supply valve 38 that regulates a supplyamount of condensed water pressurized by the pump 37 are provided in thecondensed water passage 36. A tip end portion 36 a of the condensedwater passage 36 is configured in nozzle form so that when the condensedwater supply valve 38 is opened, pressurized condensed water is injectedfrom the tip end portion 36 a in mist form. The condensed water supplyamount can be controlled by controlling an opening of the condensedwater supply valve 38.

An engine control unit (ECU) 40 is provided in the internal combustionengine 1A and configured as a computer that controls respective parts ofthe internal combustion engine 1A. The ECU 40 controls a fuel injectionamount and an injection timing using the fuel injection valves 3 duringmain operational control, and is also used to control, the EGRapparatuses 20A, 20B and the condensed water treatment apparatus 30.Signals from a large number of sensors that detect various physicalquantities are input into the ECU 40 in order to learn an operatingcondition of the internal combustion engine 1A. A crank angle sensor 41that outputs a signal corresponding to a crank angle of the internalcombustion engine 1A, an accelerator opening sensor 42 that outputs asignal corresponding to a depression amount (an accelerator opening) ofan accelerator pedal 39 provided in the internal combustion engine 1A,an air flow meter 43 that outputs a signal corresponding to an airamount, an exhaust gas A/F sensor 44 that outputs a signal correspondingto an oxygen concentration of the exhaust gas, and so on, for example,are provided in the internal combustion engine 1A as sensors relating tothe invention, and output signals from the sensors are input into theECU 40.

A feature of this embodiment is that the ECU 40 controls a supply of theEGR gas and a supply of the condensed water in a coordinated fashion.When the amount of supplied EGR gas increases, a density (an in-cylinderdensity) of gas charged into the cylinder 2 increases, thereby impairingthe diffusion of fuel spray through the cylinder 2. In other words, at aconstant fuel injection pressure, a penetration of the fuel spraydecreases steadily as the in-cylinder density increases. Accordingly,when the amount of supplied EGR gas becomes excessive, a utilizationrate of air in the cylinder 2 decreases, and as a result, amounts ofgenerated smoke and HC increase. Moreover, when the penetration is toostrong, increases in cooling loss and the amount of generated HC occuras a result of fuel adhesion to an inner wall surface of the cylinder 2.

As shown by a solid line in FIG. 2, at a constant fuel injectionpressure, the penetration of the fuel spray increases steadily as anequivalence ratio of the internal combustion engine 1A increases. Tosuppress increases in smoke and HC at a high equivalence ratio and tosuppress increases in cooling loss and the HC generation amount at a lowequivalence ratio, it is desirable to increase the penetration when theequivalence ratio is high and reduce the penetration when theequivalence ratio is low. In the control according to this embodiment,as shown by a dotted line in FIG. 2, the in-cylinder density is variedin accordance with the equivalence ratio in order to increase thepenetration when the equivalence ratio is high and reduce thepenetration when the equivalence ratio is low. Further, the in-cylinderdensity is varied by varying an EGR gas supply rate and a condensedwater supply rate in accordance with the equivalence ratio.

The EGR gas is exhaust gas generated as a result of fuel combustion, andtherefore contains carbon dioxide (CO₂) and water (H₂O) as maincomponents. Further, the main component of the condensed water is water.Hence, by varying the EGR gas supply rate and the condensed water supplyrate, a proportion of carbon dioxide and a proportion of water in thegas charged into the cylinder 2 can be varied. In other words, when theEGR gas supply rate decreases, the proportion of carbon dioxide in thecylinder 2 decreases, and when the condensed water supply rateincreases, the proportion of water in the cylinder 2 increases. Water isa low-density substance having a lower molecular weight than carbondioxide. Therefore, variation in the proportion of carbon dioxide andthe proportion of water in the cylinder 2 leads to variation in thein-cylinder density.

As shown in FIG. 3, in the control according to this embodiment, thecondensed water supply rate is increased and the EGR gas supply rate isreduced when the equivalence ratio is high relative to when theequivalence ratio is low. In so doing, the in-cylinder density decreaseswhen the equivalence ratio is high relative to when the equivalenceratio is low, and as a result, as shown by the dotted line in FIG. 2,the penetration increases when the equivalence ratio is high, anddecreases when the equivalence ratio is low.

The ECU 40 manipulates the EGR gas supply rate and the water supply raterespectively in accordance with the equivalence ratio as specified bythe calculation map shown in FIG. 3. The EGR gas supply amount can becontrolled in accordance with respective openings of the EGR valves 22,27, while the condensed water supply amount can be controlled inaccordance with an opening of the condensed water supply valve 38. TheECU 40 therefore specifies an EGR gas supply rate and a condensed watersupply rate corresponding to the equivalence ratio by referring to thecalculation map shown in FIG. 3. The ECU 40 then calculates openings ofthe respective EGR valves 22, 27 and an opening of the condensed watersupply valve 38 at which these supply rates are realized, and controlsthe respective valves 22, 27, 38 so as to realize the openings. Theopenings of the respective valves 22, 27, 38 are calculated on the basisof a specification result obtained by specifying a correspondencerelationship between the EGR gas and condensed water supply rates andthe openings of the respective valves 22, 27, 38 in advance throughprototype tests and simulations. As described above, the two EGRapparatuses 20A, 20B are used appropriately in accordance with the loadof the internal combustion engine 1A. In other words, three modes,namely a mode in which the two EGR apparatuses 20A, 20B are usedsimultaneously, a mode in which only the first EGR apparatus 20A isused, and a mode in which only the second EGR apparatus 20B is used,exist as EGR implementation modes. Hence, the openings of the respectivevalves 22, 27, 38 are calculated for each mode.

As shown in FIG. 4, a relationship between the equivalence ratio and theload (the fuel injection amount) of the internal combustion engine 1A isnot a simple proportional relationship, and varies according to whetheror not EGR is underway and the amount of EGR. In other words, the loadmay vary at a constant equivalence ratio, as shown by A in FIG. 4, andthe equivalence ratio may vary at a constant load depending on whetheror not EGR is underway, as shown by B in FIG. 4. In the controlaccording to this embodiment, the EGR gas supply rate and the condensedwater supply rate are controlled on the basis of the equivalence ratio,and therefore the in-cylinder density can be controlled accuratelywithout being affected by whether or not EGR is underway and the EGRamount.

FIG. 5 shows an example of a control routine implemented by the ECU 40.A program of the control routine shown in FIG. 5 is stored in the ECU40, read at an appropriate time, and executed repeatedly atpredetermined intervals.

In step S1, the ECU 40 calculates the fuel injection amount of theinternal combustion engine 1A. The ECU 40 specifies the acceleratoropening by referring to the output signal from the accelerator openingsensor 42, and calculates the fuel injection amount on the basis of theaccelerator opening. In step S2, the ECU 40 calculates a basicequivalence ratio on the basis of the operating condition, or in otherwords the fuel injection amount (the load), of the internal combustionengine 1A. The basic equivalence ratio is an equivalence ratio definedunivocally in accordance with the fuel injection amount and specified bya map having a characteristic such as that shown in FIG. 4. Referring tothe map shown in FIG. 4, the ECU 40 calculates the basic equivalenceratio on the basis of the fuel injection amount (the load) calculated instep S1 and whether or not EGR is being implemented. For example, asshown in FIG. 4, when the load is B and EGR is being implemented, ϕ2 iscalculated as the basic equivalence ratio, whereas when the load is Band EGR is not being implemented, ϕ1 is calculated as the basicequivalence ratio. As is commonly practiced, the equivalence ratio isdefined as the inverse of the excess air ratio, which is obtained bydividing the air-fuel ratio by the stoichiometric air-fuel ratio.

In step S3, the ECU 40 specifies the EGR gas supply rate and thecondensed water supply rate corresponding to the basic equivalence ratiocalculated in step S2 by referring to the calculation map shown in FIG.3. In step S4, the ECU 40 calculates the respective openings of the EGRvalves 22, 27 and the condensed water supply valve 38 on the basis ofthe respective supply rates specified in step S3. Note that in the modewhere the first EGR apparatus 20A and the second EGR apparatus 20B areused simultaneously, the ECU 40 calculates the respective openings ofthe two EGR valves 22, 27 and the condensed water supply valve 38.Further, in the mode where the first EGR apparatus 20A is used alone,the ECU 40 calculates the respective openings of the first EGR valve 22and the condensed water supply valve 38. Furthermore, in the mode wherethe second EGR apparatus 20B is used alone, the ECU 40 calculates therespective openings of the second EGR valve 27 and the condensed watersupply valve 38.

In step S5, the ECU 40 operates at least one of the first EGR valve 22and the second EGR valve 27 to realize the openings calculated in stepS6. In step S6, the ECU 40 operates the condensed water supply valve 38to realize the opening calculated in step S4. The current routine isthen terminated.

The openings of the respective valves 22, 27, 38 calculated in step S4of FIG. 5 are calculated on the basis of the supply rates specified bythe calculation map shown in FIG. 3. Therefore, by operating therespective valves 22, 27, 38 to the openings calculated in step S4, anEGR gas supply rate and a condensed water supply rate corresponding tothe current equivalence ratio are realized.

According to this embodiment, therefore, the in-cylinder density of theinternal combustion engine 1A decreases when the equivalence ratio ishigh and increases when the equivalence ratio is low. Hence, thein-cylinder density decreases at a high equivalence ratio, and thereforediffusion of the fuel spray can be promoted, with the result that theamounts of generated smoke and HC can be suppressed. On the other hand,the in-cylinder density increases at a low equivalence ratio, andtherefore the penetration of the fuel spray can be reduced, with theresult that increases in cooling loss and the amount of generated HCcaused by fuel adhesion to the inner wall surface of the cylinder 2 canbe suppressed. By executing the control routine shown in FIG. 5, the ECU40 functions as supply rate control means according to the invention.Further, by executing step S2 of FIG. 5, the ECU 40 functions asequivalence ratio calculating means according to the invention.

Second Embodiment

Next, referring to FIG. 6, a second embodiment of the invention will bedescribed. The second embodiment is identical to the first embodimentapart from the control content. The physical configuration of the secondembodiment can therefore be understood with reference to FIG. 1. Thesecond embodiment differs from the first embodiment in the method ofcalculating the equivalence ratio. A program of a control routine shownin FIG. 6 is stored in the ECU 40, read at an appropriate time, andexecuted repeatedly at predetermined intervals.

In step S11, similarly to the first embodiment, the ECU 40 specifies theaccelerator opening by referring to the output signal from theaccelerator opening sensor 42, and calculates the fuel injection amounton the basis of the accelerator opening. In step S12, the ECU 40 obtainsan air amount by referring to the output signal from the air flow meter43. In step S13, the ECU 40 obtains the oxygen concentration of theexhaust gas by referring to the output signal from the exhaust gas A/Fsensor 44. In step S14, the ECU 40 calculates the equivalence ratio ofthe internal combustion engine 1A on the basis of the fuel injectionamount, the air amount, and the oxygen concentration obtainedrespectively in steps S11 to S13. Processing performed in steps S15 toS18 is-identical to that of steps S3 to S6 according to the firstembodiment, shown in FIG. 5, and therefore description thereof has beenomitted.

According to the second embodiment, similarly to the first embodiment,the amounts of generated smoke and HC can be suppressed when theequivalence ratio is high, and increases in cooling loss and the amountof generated HC can be suppressed when the equivalence ratio is low. Byexecuting the control routine shown in FIG. 6, the ECU 40 functions asthe supply rate control means according to the invention. Further, byexecuting step S14 in FIG. 6, the ECU 40 functions as the equivalenceratio calculating means according to the invention.

Third Embodiment

Next, referring to FIGS. 7 to 9, a third embodiment of the inventionwill be described. The third embodiment is identical to the firstembodiment apart from the control content. The physical configuration ofthe third embodiment can therefore be understood with reference toFIG. 1. The ECU 40 controls a fuel injection pressure of the internalcombustion engine 1A, or in other words an internal pressure of thecommon rail 5, in accordance with the operating condition of theinternal combustion engine 1A. When the fuel injection pressure varies,the penetration of the fuel spray is affected thereby, and it maytherefore be impossible to obtain an appropriate penetration simply byvarying the in-cylinder density in a similar manner to the first orsecond embodiment. Hence, in the third embodiment, an appropriatepenetration is obtained by calculating the EGR gas supply rate and thecondensed water supply rate on the basis of the fuel injection pressureas well as the equivalence ratio.

Equation 1, shown below, which is called as “Hiroyasu's formula”, iswidely available as an empirical formula defining a relationship betweenthe fuel injection pressure and the penetration strength.

S=2.95×((P _(inj) −P _(a))/ρ_(a))^(0.25)×(d ₀ ·t)^(0.5)  1

Here, S denotes the penetration strength, P_(inj) denotes the fuelinjection pressure, P_(n) denotes an in-cylinder atmospheric pressure,ρ_(a) denotes the in-cylinder density, d₀ denotes an injection holediameter, and t denotes time.

The in-cylinder density ρ_(a) and the in-cylinder atmospheric pressureP_(a) are commensurate, and therefore, when A is set as a coefficient,Equation 1 may be seen as Equation 2, shown below.

S=A×((P _(inj) −P _(a))/ρ_(a))^(0.25) =A×(P _(inj) /P _(a)−1)^(0.25)  2

By solving Equation 2 with respect to the in-cylinder atmosphericpressure P_(a) and setting B as a coefficient, Equation 3 is obtained.

P _(a) =B×P _(inj)/(S ⁴+1)  3

Furthermore, the in-cylinder density ρ_(a) and the in-cylinderatmospheric pressure P_(a) are commensurate, as described above, andtherefore, when C is set as a coefficient, Equation 3 may be seen asEquation 4, shown below.

ρ_(a) =C×P _(inj)/(S ⁴+1)  4

Here, a desired penetration strength is determined for each equivalenceratio (see FIG. 2) and inserted into Equation 4. As a result, arelationship between the fuel injection pressure and the in-cylinderdensity at which to obtain the desired penetration strength is obtainedfor each equivalence ratio. By ordering these three parameters, i.e. theequivalence ratio, the fuel injection pressure, and the in-cylinderdensity, a map shown in FIG. 7 is obtained.

In the third embodiment, the in-cylinder density corresponding to thecurrent equivalence ratio and fuel injection pressure is specified byreferring to a map such as that shown in FIG. 7, on which thein-cylinder density is given using the equivalence ratio and the fuelinjection pressure as variables. The respective openings of the EGRvalves 22, 27 and the condensed water supply valve 38 are thendetermined so as to obtain an EGR gas supply rate and a condensed watersupply rate corresponding to the specified in-cylinder density,whereupon the respective valves 22, 27, 38 are operated so as to obtainthe determined openings.

A program of a control routine shown in FIG. 8 is stored in the ECU 40,read at an appropriate time, and executed repeatedly at predeterminedintervals. In step S21, the ECU 40 calculates the equivalence ratio ofthe internal combustion engine 1A. The equivalence ratio may becalculated using either the method of the first embodiment or the methodof the second embodiment. In step S22, the ECU 40 obtains the fuelinjection pressure. The ECU 40 obtains the fuel injection pressure onthe basis of an output signal from a pressure sensor, not shown in thedrawings, attached to the common rail 5.

In step S23, the ECU 40 specifies the in-cylinder density correspondingto the current equivalence ratio and fuel injection pressure on thebasis of the calculation map shown in FIG. 7, for example. In step S24,the ECU 40 calculates openings of the EGR valves 22, 27 corresponding tothe in-cylinder density specified in step S23 by referring to acalculation map shown in FIG. 9, for example. In step S25, the ECU 40calculates an opening of the condensed water supply valve 38corresponding to the in-cylinder density specified in step S23 byreferring to the same calculation map. The calculation map of FIG. 9corresponds to an operating region where the ECU 40 uses the first EGRapparatus 20A alone. Note that calculation maps having similarcharacteristics to FIG. 9 are prepared respectively for the mode inwhich the two EGR apparatuses 20A, 20B are used simultaneously and themode in which the second EGR apparatus 20B is used alone. In step S24and step S25, the calculation map corresponding to the current operatingregion is selected, and the respective openings are calculated on thebasis of the selected calculation map.

In step S26, the ECU 40 operates at least one of the first EGR valve 22and the second EGR valve 27 so as to obtain the opening calculated instep S24. In step S27, the ECU 40 operates the condensed water supplyvalve 38 so as to obtain the opening calculated in step S25. The currentroutine is then terminated.

On the calculation maps used in steps S24 and S25 of FIG. 8, theopenings of the respective valves 22, 28, 38 are calculated so as torealize the EGR gas supply rate and the condensed water supply rate atwhich to obtain the in-cylinder density specified by the map shown inFIG. 7. The in-cylinder density specified by the map shown in FIG. 7,similarly to that of FIG. 3, decreases steadily as the equivalence ratioincreases. In other words, the in-cylinder density of the internalcombustion engine 1A decreases at a high equivalence ratio and increasesat a low equivalence ratio. The map of FIG. 7 defines the in-cylinderdensity at which an appropriate penetration strength is obtained on thebasis of the equivalence ratio and the fuel injection pressure. Thepenetration of the fuel spray can therefore be made appropriate evenwhen the fuel injection pressure varies. By executing the controlroutine shown in FIG. 8, the ECU 40 functions as the supply rate controlmeans according to the invention. Further, by executing step S21 of FIG.8, the ECU 40 functions as the equivalence ratio calculating meansaccording to the invention.

Fourth Embodiment

Next, referring to FIGS. 10 and 11, a fourth embodiment of the inventionwill be described. The fourth embodiment is identical to the firstembodiment apart from the control content. The physical configuration ofthe fourth embodiment can therefore be understood with reference toFIG. 1. In the fourth embodiment, as shown in FIG. 10, the EGR gassupply rate and the condensed water supply rate are controlled so thatin a case where the equivalence ratio is lower than a predeterminedvalue Φt, the water ratio is lower before warm-up of the internalcombustion engine 1A is complete than after warm-up is complete.

A program of a control routine shown in FIG. 11 is stored in the ECU 40,read at an appropriate time, and executed repeatedly at predeterminedintervals. In step S31, the ECU 40 calculates the equivalence ratio ofthe internal combustion engine 1A. The equivalence ratio may becalculated using either the method of the first embodiment or the methodof the second embodiment. In step S32, the ECU 40 calculates theopenings of the EGR valves 22, 27. In step S33, the ECU 40 calculatesthe opening of the condensed water supply valve 38. Any one of themethods described in the first to third embodiments may be employed tocalculate the respective openings in steps S32 and S33.

In step S34, the ECU 40 determines whether or not the equivalence ratiocalculated in step S31 is smaller than the predetermined value ϕt. Thepredetermined value ϕt is set in consideration of a degree of an adverseeffect caused by fuel adhesion to the inner wall surface of the cylinder2 prior to the completion of warm-up, to be described below. When theequivalence ratio is smaller than the predetermined value ϕt, or inother words when the equivalence ratio is lower than the predeterminedvalue ϕt, the routine advances to step S35. When the equivalence ratioequals or exceeds the predetermined value ϕt, the routine skips step S35and step S36 and advances to step S37.

In step S35, the ECU 40 determines whether or not warm-up of theinternal combustion engine 1A is complete. The ECU 40 determines thatwarm-up is not yet complete when, for example, a cooling watertemperature representing the temperature of the internal combustionengine 1A is lower than 80 degrees centigrade. When warm-up is not yetcomplete, the routine advances to step S36. When warm-up of the internalcombustion engine 1A is complete, the routine skips step S36 andadvances to step S37.

In step S36, the ECU 40 corrects the respective openings of the EGRvalves 22, 27 and the condensed water supply valve 38 calculated in stepS32 and step S33. The respective openings are corrected by correctingthe openings of the EGR valves 22, 27 toward an open side and correctingthe opening of the condensed water supply valve 38 toward a closed side.Correction amounts are set in accordance with the equivalence ratio soas to obtain pre-warm-up completion supply rates, as shown in FIG. 10.

In step S37, the ECU 40 operates at least one of the first EGR valve 22and the second EGR valve 27 so as to obtain either the openingcalculated in step S32 or the corrected opening corrected in step S36.In step S38, the ECU 40 operates the condensed water supply valve 38 soas to obtain either the opening calculated in step S33 or the correctedopening corrected in step S36. The current routine is then terminated.

According to the fourth embodiment, when the equivalence ratio is lowerthan the predetermined value ϕt and warm-up is not yet complete, theopenings of the EGR valves 22, 27 are corrected toward the open side andthe opening of the condensed water supply valve 38 is corrected towardthe closed side in step S36 of FIG. 11. Accordingly, the condensed watersupply rate when the equivalence ratio is lower than the predeterminedvalue ϕt becomes lower before warm-up is complete than after warm-up iscomplete. Hence, the in-cylinder density at a low equivalence ratioprior to the completion of warm-up becomes higher than the in-cylinderdensity following the completion of warm-up, with the result that thepenetration of the fuel spray can be reduced in comparison with thepenetration following the completion of warm-up. Therefore, fueladhesion to the inner wall surface of the cylinder 2 prior to thecompletion of warm-up can be suppressed, and as a result, the amount ofHC generated prior to the completion of warm-up can be reduced. Byexecuting the control routine shown in FIG. 11, the ECU 40 functions asthe supply rate control means according to the invention. Further, byexecuting step S31 of FIG. 11, the ECU 40 functions as the equivalenceratio calculating means according to the invention.

Fifth Embodiment

Next, referring to FIGS. 12 to 14, a fifth embodiment of the inventionwill be described. As shown in FIG. 12, the fifth embodiment is appliedto an internal combustion engine 1B that differs from the internalcombustion engine 1A of FIG. 1 in the EGR system and a condensed watersupply location. Configurations of the internal combustion engine 1Bthat are shared with the internal combustion engine 1A are illustratedin FIG. 12 using identical reference symbols, and description thereofhas been omitted.

The internal combustion engine 1B includes the first EGR apparatus 20Aand a second EGR apparatus 20B′. The second EGR apparatus 20B′ isprovided with a carbon dioxide separator (referred to hereafter as aseparator) 50 serving as separating means that separates carbon dioxidefrom the EGR gas, a bypass passage 51 provided on the second EGR passage26 so as to bypass the separator 50, and a flow distributionmodification valve 52 provided in a convergence position between thebypass passage 51 and the second EGR passage 26 so as to be capable ofcontinuously modifying a flow distribution between a flow through thebypass passage 51 and a flow through the separator 50. The separator 50is provided in the second EGR passage 26 on a downstream side of thesecond EGR cooler 28. A conventional apparatus capable of separatingcarbon dioxide using one of various methods such as a chemicalseparation method or a physical adsorption method may be applied as theseparator 50. The bypass passage 51 is connected between the second EGRcooler 28 and the separator 50 on an upstream side, and connectedbetween the separator 50 and the second EGR valve 27 on a downstreamside.

The flow distribution modification valve 52 is capable of modifying theflow distribution from a condition in which the separator 50 is closedso that the flow through the separator 50 remains at zero, whereby allof the EGR gas flowing through the second EGR passage 26 flows throughthe bypass passage 51, to a condition in which the bypass passage 51 isclosed so that the flow through the bypass passage 51 remains at zero,whereby all of the EGR gas flowing through the second EGR passage 26flows through the separator 50. By operating the flow distributionmodification valve 52, the amount of carbon dioxide separated from theEGR gas can be adjusted. Hence, the bypass passage 51 and the flowdistribution modification valve 52 function in combination as adjustingmeans according to the invention.

The condensed water supply mechanism 35 is configured such that the tipend portion 36 a of the condensed water passage 36 is connected to thesecond EGR passage 26 between the flow distribution modification valve52 and the second EGR valve 27. As a result, the condensed water storedin the condensed water tank 31 can be supplied to the second EGR passage26 between the flow distribution modification valve 52 and the secondEGR valve 27. As described above, the condensed water supply amount canbe controlled by operating the condensed water supply valve 38. Byoperating the flow distribution modification valve 52 and the condensedwater supply valve 38 respectively, the proportions of water and carbondioxide in the EGR gas can be modified. Hence, the separator 50, thebypass passage 51, the flow distribution modification valve 52, and thecondensed water supply mechanism 35 together constitute componentproportion modifying means according to the invention.

The ECU 40 controls the in-cylinder density by modifying the proportionsof water and carbon dioxide in the EGR gas in accordance with theequivalence ratio of the internal combustion engine 1B. Similarly to thefirst to fourth embodiments described above, the in-cylinder density iscontrolled so as to decrease at a high equivalence ratio and increase ata low equivalence ratio. More specifically, the ECU 40 calculatesproportions of water (H₂O) and carbon dioxide (CO₂) in the EGR gascorresponding to the equivalence ratio of the internal combustion engine1B on the basis of the calculation map shown in FIG. 13, and thenoperates the flow distribution modification valve 52 and the condensedwater supply valve 38 so that the calculated proportions can berealized.

FIG. 14 shows an example of a control routine implemented by the ECU 40.A program of the control routine shown in FIG. 14 is stored in the ECU40, read at an appropriate time, and executed repeatedly atpredetermined intervals.

In step S41, the ECU 40 calculates the fuel injection amount of theinternal combustion engine 1B. Similarly to the embodiments describedabove, the ECU 40 specifies the accelerator opening by referring to theoutput signal from the accelerator opening sensor 42, and calculates thefuel injection amount on the basis of the accelerator opening. In stepS42, the ECU 40 calculates the basic equivalence ratio on the basis ofthe operating condition, or in other words the fuel injection amount(the load), of the internal combustion engine 1B. Similarly to the firstembodiment, the basic equivalence ratio is an equivalence ratio definedunivocally in accordance with the fuel injection amount and specified bya map having a characteristic such as that shown in FIG. 4. Referring tothe map shown in FIG. 4, the ECU 40 calculates the basic equivalenceratio on the basis of the fuel injection amount (the load) calculated instep S41 and whether or not EGR is being implemented.

In step S43, the ECU 40 specifies the proportions of water and carbondioxide in the EGR gas corresponding to the equivalence ratio calculatedin step S42 by referring to a calculation map shown in FIG. 13. In stepS44, the ECU 40 calculates a flow distribution between the flow throughthe separator 50 and the flow through the bypass passage 51 so as toobtain the proportions of water and carbon dioxide specified in stepS43. In step S45, the ECU 40 calculates an opening of the condensedwater supply valve 38 at which the proportions of water and carbondioxide specified in step S43 are obtained. The flow distribution andthe opening are calculated in step S44 and step S45, respectively, onthe basis of a calculation map, not shown in the drawings, determined inadvance through prototype tests and simulations. Note that thisembodiment is applied only to either the mode in which the two EGRapparatuses 20A, 20B′ are used simultaneously or the mode in which thesecond EGR apparatus 20B′ is used alone, and therefore the calculationmap not shown in the drawings is prepared in relation to each of thesetwo modes.

In step S46, the ECU 40 operates the flow distribution modificationvalve 52 so as to realize the flow distribution calculated in step S44.In step S47, the ECU 40 operates the condensed water supply valve 38 soas to obtain the opening calculated in step S45. The current routine isthen terminated.

According to the control routine shown in FIG. 14, when EGR isimplemented, the proportions of water and carbon dioxide in the EGR gassupplied to the cylinder 2 of the internal combustion engine 1B arecontrolled to the proportions shown in FIG. 13. More specifically, at ahigh equivalence ratio, the proportion of water in the EGR gas is higherand the proportion of carbon dioxide in the EGR gas is lower than at alow equivalence ratio. In other words, similarly to the embodimentsdescribed above, the in-cylinder density of the internal combustionengine 1B decreases at a high equivalence ratio and increases at a lowequivalence ratio. Hence, the in-cylinder density decreases at a highequivalence ratio, and therefore diffusion of the fuel spray can bepromoted, with the result that the amounts of generated smoke and HC canbe suppressed. On the other hand, the in-cylinder density increases at alow equivalence ratio, and therefore the penetration of the fuel spraycan be reduced, with the result that increases in cooling loss and theamount of generated HC caused by fuel adhesion to the inner wall surfaceof the cylinder 2 can be suppressed. By executing the control routineshown in FIG. 14, the ECU 40 functions as the component proportioncontrol means according to the invention. Further, by executing step S42of FIG. 14, the ECU 40 functions as the equivalence ratio calculatingmeans according to the invention.

Sixth Embodiment

Next, referring to FIG. 15, a sixth embodiment of the invention will bedescribed. The sixth embodiment is identical to the fifth embodimentapart from the control content. The physical configuration of the sixthembodiment can therefore be understood with reference to FIG. 14. Thesixth embodiment differs from the fifth embodiment in the method ofcalculating the equivalence ratio. A program of a control routine shownin FIG. 15 is stored in the ECU 40, read at an appropriate time, andexecuted repeatedly at predetermined intervals.

In step S51, similarly to the fifth embodiment, the ECU 40 specifies theaccelerator opening by referring to the output signal from theaccelerator opening sensor 42, and calculates the fuel injection amounton the basis of the accelerator opening. In step S52, the ECU 40 obtainsthe air amount by referring to the output signal from the air flow meter43. In step S53, the ECU 40 obtains the oxygen concentration of theexhaust gas by referring to the output signal from the exhaust gas A/Fsensor 44. In step S54, the ECU 40 calculates the equivalence ratio ofthe internal combustion engine 1B on the basis of the fuel injectionamount, the air amount, and the oxygen concentration obtainedrespectively in steps S51 to S53. Processing performed in steps S55 toS59 is identical to that of steps S43 to S47 according to the fifthembodiment, shown in FIG. 14, and therefore description thereof has beenomitted.

According to the sixth embodiment, similarly to the fifth embodiment,the amounts of generated smoke and HC can be suppressed when theequivalence ratio is high, and increases in cooling loss and the amountof generated HC can be suppressed when the equivalence ratio is low. Byexecuting the control routine shown in FIG. 15, the ECU 40 functions asthe component proportion control means according to the invention.Further, by executing step S54 in FIG. 15, the ECU 40 functions as theequivalence ratio calculating means according to the invention.

The invention is not limited to the embodiments described above, and maybe implemented in various embodiments within the scope of the spirit ofthe invention. In the first to fourth embodiments, condensed water isused as the low density substance, but using condensed water or water asthe low density substance is merely an example. By supplying the lowdensity substance to the intake system, the in-cylinder density can bevaried. The object of the invention can be achieved likewise using aninert substance that has a lower molecular weight than carbon dioxide(molecular weight 44) and does not adversely affect combustion, such ashelium, nitrogen, or neon, for example, instead of water as the lowdensity substance.

In the first to fourth embodiments, condensed water generated in theexhaust system of the internal combustion engine is supplied to thecylinder, thereby eliminating the need to prepare and resupply a lowdensity substance. Moreover, the supplied condensed water is vaporizedin the cylinder, thereby reducing the combustion temperature. At a highequivalence ratio, therefore, the condensed water supply rate isincreased instead of reducing the EGR gas supply rate, and as a result,a NO_(X) generation suppression effect can be maintained whilesuppressing an increase in the in-cylinder density.

In the first to fourth embodiments, the EGR gas is supplied to thecylinder through the intake passage, but in a modified embodiment, theEGR gas may be supplied to the cylinder directly. Further, in the firstto fourth embodiments, the condensed water is supplied to the cylinderthrough the intake passage, but instead, the condensed water may besupplied to the cylinder through the exhaust passage during a valveoverlap period using a similar method to so-called internal EGR.Furthermore, the condensed water may be supplied to the cylinderdirectly. When an inert substance such as those mentioned above is usedas the low density substance instead of condensed water or water, theinert substance may be supplied to the cylinder either indirectlythrough the intake passage or the exhaust passage or directly, i.e.without passing through the intake passage or the exhaust passage.

In the fifth and sixth embodiments, the proportions of water and carbondioxide in the EGR gas are modified by supplying the condensed waterusing the condensed water supply mechanism 35 while separating carbondioxide from the EGR gas using the separator 50. This is merely anexample, however, and instead, for example, the invention may beimplemented in an embodiment where carbon dioxide is added whileseparating water from the EGR gas. In this embodiment, a combination ofmeans for separating water from the EGR gas and means for adding carbondioxide corresponds to the component proportion modifying meansaccording to the invention. In the fifth and sixth embodiments, theproportions of water and carbon dioxide in the EGR gas are modifiedusing the condensed water generated in the exhaust system of theinternal combustion engine, but using condensed water is merely anexample, and instead, the invention may be implemented in an embodimentwhere water other than condensed water is prepared and added to the EGRgas. Similarly to the first to fourth embodiments, when condensed wateris used, the need to prepare and resupply a low density substance can beeliminated. Moreover, the supplied condensed water is vaporized in thecylinder, thereby reducing the combustion temperature. At a highequivalence ratio, therefore, the proportion of water in the EGR gas isincreased instead of reducing the proportion of carbon dioxide in theEGR gas, and as a result, the NO_(X) generation suppression effect canbe maintained while suppressing an increase in the in-cylinder density.

The control executed in the fifth and sixth embodiments may be modifiedto similar control to that of the third or fourth embodiment. As similarcontrol to the third embodiment, the ECU 40 may calculate the proportionof water in the EGR gas and the proportion of carbon dioxide in the EGRgas on the basis of the fuel injection pressure as well as theequivalence ratio, and then operate the flow distribution modificationvalve 52 and the condensed water supply valve 38 respectively on thebasis of the calculation result. Specific processing content isidentical to the third embodiment. In other words, the ECU 40 calculatesthe in-cylinder density on the basis of the fuel injection pressure aswell as the equivalence ratio by referring to a map such as that shownin FIG. 7, and calculates the proportions of water and carbon dioxide atwhich the calculated in-cylinder density is realized. As a result, thepenetration of the fuel spray can be made appropriate in a similarmanner to the third embodiment.

Further, as similar control to the fourth embodiment, the ECU 40 mayoperate the flow distribution modification valve 52 and the condensedwater supply valve 38 respectively so that the proportion of carbondioxide in the EGR gas in a case where the equivalence ratio of theinternal combustion engine 1B is lower than the predetermined value islower before warm-up of the internal combustion engine 1B is completethan after warm-up of the internal combustion engine 1B is complete.Specific processing content is identical to the fourth embodiment. Inother words, when the equivalence ratio is lower than the predeterminedvalue ϕt and warm-up is not yet complete, as shown in FIG. 10, the ECU40 corrects an operation amount of the flow distribution modificationvalve 52 in a direction for increasing the flow distribution of thebypass passage 51, and corrects the opening of the condensed watersupply valve 38 toward the closed side. Accordingly, the proportion ofcarbon dioxide in the EGR gas in a case where the equivalence ratio islower than the predetermined value ϕt becomes lower before warm-up iscomplete than after warm-up is complete, and therefore the in-cylinderdensity at a low equivalence ratio before warm-up is complete becomeshigher than the in-cylinder density after warm-up is complete. As aresult, similarly to the fourth embodiment, the amount of HC generatedprior to the completion of warm-up can be reduced.

In the above embodiments, two EGR apparatuses having different loopconfigurations are provided, but the invention may be implemented in anembodiment where only one EGR apparatus is provided. The internalcombustion engine according to the above embodiments is configured as adiesel engine, but the invention is not limited to being applied to adiesel engine, and may be applied to any internal combustion engine inwhich fuel is injected into a cylinder, such as an in-cylinder directinjection type spark ignition internal combustion engine that usesgasoline as fuel. Furthermore, application of the invention is notaffected by the presence or absence of a turbocharger, and therefore theinvention may also be applied to a naturally aspirated internalcombustion engine.

1-5. (canceled)
 6. A control apparatus for an internal combustion engineconfigured to inject fuel into a cylinder, the internal combustionengine including an EGR apparatus configured to supply a part of exhaustgas into the cylinder as EGR gas, and component proportion modifyingmeans configured to modify proportions of water and carbon dioxide inthe EGR gas, the control apparatus comprising an electronic control unitconfigured to (i) calculate an equivalence ratio of the internalcombustion engine, and (ii) control the component proportion modifyingmeans such that, when the equivalence ratio is high, a proportion ofwater in the EGR gas increases and a proportion of carbon dioxide in theEGR gas decreases relative to when the equivalence ratio is low.
 7. Thecontrol apparatus according to claim 6, wherein the electronic controlunit is configured to calculate the equivalence ratio on the basis of anoperating condition of the internal combustion engine.
 8. The controlapparatus according to claim 6, wherein the electronic control unit isconfigured to control the component proportion modifying means such thatthe proportion of carbon dioxide in the EGR gas in a case where theequivalence ratio is lower than a predetermined value becomes lowerbefore warm-up of the internal combustion engine is complete than afterwarm-up of the internal combustion engine is complete.
 9. The controlapparatus according to claim 6, wherein the electronic control unit isconfigured to (i) calculate the proportion of water in the EGR gas andthe proportion of carbon dioxide in the EGR gas on the basis of a fuelinjection pressure as well as the equivalence ratio, and control thecomponent proportion modifying means on the basis of an obtainedcalculation result.
 10. The control apparatus according to claim 6,wherein separating means for separating carbon dioxide from the EGR gas,adjusting means capable of adjusting an amount of carbon dioxideseparated from the EGR gas, and a condensed water supply mechanism thatadds condensed water generated in an exhaust system of the internalcombustion engine to the EGR gas from which carbon dioxide has beenseparated by the separating means are provided as the componentproportion modifying means.